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Simulation Explores Spread of Virus in an Airplane

Posted Thu March 17, 2005 @10:28AM

Occupational Hazards has posted an article on the use of CFD to simulate the spread of virus within the cabin of a commercial airliner.

The question of infectious diseases spreading through an aircraft's ventilation system is a serious concern to air travelers and flight crews. Increased interest in this issue by airline employees prompted the Federal Aviation Administration (FAA) to sponsor a study by the National Institute for Occupational Safety and Health (NIOSH) to consider new methods to investigate the potential for airborne disease transmission on commercial flights.

Because of the difficulty of testing in an actual aircraft cabin during flight conditions, the primary focus of this project has been to perform numerical simulation of the cabin airflow. A numerical simulation can predict the effect of conditions that could never be tested, and many different conditions can be examined in far less time and at a lower cost than would be required for physical testing. In addition, simulation provides results at every point in the computational domain while testing results are limited to the areas and conditions that can be measured.

Of course, a critical challenge in every computer simulation is ensuring that the simulation accurately predicts real world observations. Engineers began their simulation effort using the traditional k-epsilon turbulence model. Correlating the predictions of these simulations with recent experimental measurements using a hot wire anemometer showed that the traditional turbulence model substantially under-predicted the turbulence in the cabin. NIOSH and Boeing engineers worked together to increase the accuracy of the model using state-of-the-art CFD codes. This work drew on Boeing's experience in modeling a wide range of airflow problems in their broad range of aerospace products. For example, Boeing has long used CFD to design cabin sections, but has more recently begun creating very large models of the entire cabin. In designing such critical areas of the aircraft, simulation accuracy is essential, so considerable time has been spent evaluating the effectiveness of different physical models.

The ideal approach is to model the entire cabin in an environment that would have made it possible to utilize the latest and most accurate turbulence models. But that wasn't an option when the team started so they used another approach that they thought would be nearly as effective. They began with a very simplified version of the cabin geometry that was similar in Reynolds number to an actual cabin. They used this simplified model to explore the physics of flow within the cabin using Fluent CFD software. Fluent offers several turbulence models that could be used in airflow studies. For instance, one model is the large eddy simulation (LES) model, in which time averaging is applied to only the smallest turbulent eddies, those that are smaller than a typical cell size. Larger eddies are computed directly in this time-dependent model. Aircraft ventilation analysts discovered that the traditional model could be adjusted to duplicate the turbulence levels found in the LES with the User Defined Functions feature in Fluent. They continue to use the modified traditional model for further studies because it is less computationally intensive and therefore provides results in less time.